This application claims priority from Japanese Patent Application No. 2007-053275 filed Mar. 2, 2007, which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a technology of a zoom lens.
2. Description of the Related Art
Recently, various electronic imaging devices such as digital still cameras, video cameras, and surveillance camera have become common. Most of the electronic imaging devices include a zoom lens as an imaging lens. With the miniaturization of recent electronic imaging devices, further miniaturization of the zoom lens has been demanded, and many compact and wide-angle zoom lenses have been suggested to meet the demand (see Japanese Patent No. 3600870 and Japanese Patent Application Laid-open Publication Nos. 2006-119574 and 2002-277737).
A wide-angle zoom lens that has a large aperture and can monitor a dark place over a wider range has been preferable for a lens of the surveillance camera. However, due to the advance of megapixel resolution of imaging sensors such as a charge coupled device (CCD) and a complementary metal oxide semiconductor (CMOS), a megapixel-compatible lens for capturing finer characteristics of a subject has been expected, and a zoom lens adaptable to the megapixel resolution of the imaging sensors has been provided (see homepage of CBC Co., Ltd., URL:    http://www.computar.jp/cbc_program/OUT_FILEUPLOAD_B/49.pdf)
The megapixel-compatible lens for the electronic imaging devices must correct well various aberrations occurring around a screen in order to capture finer characteristics of a subject.
However, the zoom lenses disclosed in the above three Japanese patent documents are unsuitable for the megapixel-compatible lens in the electronic imaging devices since sufficient correction the aberrations, such as axial chromatic and spherical aberrations, is difficult.
Further, although the lens disclosed in the above homepage of CBC Co., Ltd. is megapixel-compatible, the angle of view at the wide-angle end thereof is only 76°. Therefore, when a surveillance camera employing the lens disclosed in the above homepage of CBC Co., Ltd. is set at a corner of a room, there are blind spots due to the narrow angle of view, necessitating more than two cameras to eliminate the blind spots.